A gas turbine engine (GTE) may include multiple sets of nozzles that each deliver burn fuel to a combustion chamber within the GTE. These sets of nozzles may include, for example, a primary set of atomizer nozzles and a secondary set of air blast nozzles. During GTE start-up, it is generally desirable to provide a greater volume of fuel flow to the atomizer nozzles than to the air blast nozzles (i.e., “bias up” atomizer fuel flow) to achieve optimal engine lightoff conditions. However, after GTE start-up, it is generally desirable to provide substantially equal flow to the atomizer nozzles and the air blast nozzles to achieve an evenly distributed burn spray pattern in the combustion chamber. To address this need, fuel divider systems have been developed that bias up burn fuel supplied to the atomizer nozzles as a function of total metered burn fuel supplied to the fuel divider system. When little burn fuel is supplied to the system during GTE start-up, the fuel divider system provides a relatively large flow bias in favor of the atomizer nozzles. This bias decreases as the total burn fuel supplied to the system increases and ultimately disappears at an upper threshold flow rate. In this manner, the fuel divider system biases up fuel flow to the atomizer nozzles during engine lightoff conditions, while providing an equalized flow to the atomizer nozzles and the air blast nozzles during moderate to high flow engine run conditions, such as engine cruise.
Fuel divider systems of the type described above may further include an ecology valve that is fluidly coupled to the atomizer and air blast nozzles. Upon cessation of GTE operation, the ecology valve removes a predetermined volume of burn fuel from the engine fuel manifold. In so doing, the ecology valve decreases the volume of fuel available for vaporization to the atmosphere and deters coking of the atomizer and air blast nozzles. The ecology valve then returns the withdrawn fuel to the fuel engine manifold when GTE operation is again initiated.
Although addressing the need to bias up fuel flow to the atomizer nozzles during engine start-up, conventional fuel divider systems of the type described above are limited in certain respects. As explained above, such fuel divider systems bias up the volume burn fuel supplied to the atomizer nozzles as a function of the total burn fuel supplied to the system. Consequently, such fuel divider systems also bias up burn fuel supplied to the atomizer nozzles during certain post start-up conditions, such as flight idle, wherein relatively little burn fuel is supplied to the GTE through the fuel divider system. Unequal fuel distribution during such low flow post start-up conditions may result in an uneven burn spray pattern, which, in turn, may lead to heat-induced engine combustor distress in areas adjacent the atomizer nozzles. As a further limitation, fuel divider systems of the type described above permit the ecology valve to move, and thus reintroduced previously-withdrawn burn fuel to the engine fuel manifold, during GTE start-up. By prematurely introducing burn fuel to the engine fuel manifold, the ecology valve may alter the scheduled fuel distribution between the atomizer and air blast nozzles and thereby comprise ideal GTE start flow conditions.
It is thus desirable to provide a fuel divider system for use in conjunction with a gas turbine engine that biases up fuel flow to a primary set of nozzles (e.g., atomizer nozzles) during engine start-up conditions, while providing substantially equal flow to primary and secondary sets of nozzles during low flow post start-up engine conditions, such as flight idle. It would also be desirable if, in embodiments wherein the fuel divider system employed an ecology valve, the fuel divider system prevented ecology valve movement during engine start-up procedures. Preferably, in certain embodiments, the fuel divider system would assumed the form of a closed-loop hydromechanical systems so as to eliminate the need for external controllers and electronic components, such as sensors, wire harnesses, and the like. Other desirable features and characteristics of the present invention will become apparent from the subsequent Detailed Description and the appended claims, taken in conjunction with the accompanying drawings and this Background.